A light emitting diode (LED) is preferred and popularized as an environment-friendly product.
The LED is manufactured by a semiconductor manufacturing process. Presently, research and development on the LED is being conducted actively.
Recently, due to various positive features of the LED, interest in the LED for lighting, having optical characteristics suitable for replacing conventional incandescent bulbs, is increasing. Accordingly, products in which the LED replaces a fluorescent lamp or incandescent bulb in conventional lighting systems are being put on the market.
Nowadays, LED lighting systems having brightness comparable to a level of conventional lighting systems are being developed. However, several research projects are still being conducted in many fields including an LED, a package, an optical system including the LED, and an LED control circuit.
Additionally, use of a high-output and high-brightness LED is increasing as an external pilot lamp of a car, for safer driving.
LED lamps for cars include an LED head lamp (H/L), a rear combination lamp (RCL), a center high mounted stop lamp (CHMSL), a daytime running lamp (DRL), a position lamp, and the like. An LED package mounting the RCL and the DRL occupies a main part.
With the increase in use of the LEDs for cars, when a plurality of LEDs is applied, a small number of LEDs are serially connected into strings and a plurality of the strings of LEDs is connected in parallel.
When constituting an LED array using the above parallel configuration, a current difference may be generated between respective parallel strings due to a current of the serially connected LEDs.
Since the LED is driven by a current, a constant current supply is necessary to maintain constant brightness.
Generally, a constant current driving integrated circuit (IC) or a microprocessor is used to achieve a constant current driving circuit. However, such devices may lead to an increase in manufacturing costs.
In general LED arrays, although a constant current source is used, a current flowing to each respective string may be different due to a deviation of current (Vf) of the LEDs connected to each of the respective strings.